Esbuild version 0.8.38 introduces subtle but potentially impactful changes compared to its predecessor, version 0.8.37. Both versions maintain the core functionality of esbuild as an extremely fast JavaScript bundler and minifier, licensed under the MIT license and available via its GitHub repository. The key distinction lies in the increased unpackedSize of the newer version -- 69309 bytes compared to the older version's 64262 bytes. This suggests the inclusion of new features, bug fixes, or optimizations that add to the overall package size and may improve performance or resolve compatibility issues. For developers using esbuild, this could mean better handling of specific JavaScript constructs or enhanced minification capabilities.
Importantly, version 0.8.38 was released on January 31, 2021, a day after version 0.8.37. This rapid release cycle indicates active development and a commitment to addressing user needs and discovered issues quickly. Developers should consider upgrading to version 0.8.38 to leverage the potential benefits of these improvements, especially if they have encountered any limitations or bugs in the previous version. However, it is advisable to thoroughly test the new version to confirm that it aligns with the project-specific requirements to avoid unexpected behavior, as with any update. The increased unpackedSize might also slightly affect build times, memory footprint, and CDN bandwidth.
All the vulnerabilities related to the version 0.8.38 of the package
esbuild enables any website to send any requests to the development server and read the response
esbuild allows any websites to send any request to the development server and read the response due to default CORS settings.
esbuild sets Access-Control-Allow-Origin: * header to all requests, including the SSE connection, which allows any websites to send any request to the development server and read the response.
https://github.com/evanw/esbuild/blob/df815ac27b84f8b34374c9182a93c94718f8a630/pkg/api/serve_other.go#L121 https://github.com/evanw/esbuild/blob/df815ac27b84f8b34374c9182a93c94718f8a630/pkg/api/serve_other.go#L363
Attack scenario:
http://malicious.example.com).fetch('http://127.0.0.1:8000/main.js') request by JS in that malicious web page. This request is normally blocked by same-origin policy, but that's not the case for the reasons above.http://127.0.0.1:8000/main.js.In this scenario, I assumed that the attacker knows the URL of the bundle output file name. But the attacker can also get that information by
/index.html: normally you have a script tag here/assets: it's common to have a assets directory when you have JS files and CSS files in a different directory and the directory listing feature tells the attacker the list of files/esbuild SSE endpoint: the SSE endpoint sends the URL path of the changed files when the file is changed (new EventSource('/esbuild').addEventListener('change', e => console.log(e.type, e.data)))The scenario above fetches the compiled content, but if the victim has the source map option enabled, the attacker can also get the non-compiled content by fetching the source map file.
npm inpm run watchfetch('http://127.0.0.1:8000/app.js').then(r => r.text()).then(content => console.log(content)) in a different website's dev tools.Users using the serve feature may get the source code stolen by malicious websites.